• 상하수도학회지
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• 제29권1호
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• pp.11-21
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• 2015

When designing Water Distribution System (WDS), determination of life cycle for WDS needs to be preceded. And designer should conduct comprehensive design including maintenance and management strategies based on the determined life cycle. However, there are only a few studies carried out until now, and criteria to determine life cycle of WDS are insufficient. Therefore, methodology to determine life cycle of WDS is introduced in this study by using Life Cycle Energy Analysis (LCEA). LCEA adapts energy as an environmental impact criterion and calculates all required energy through the whole life cycle. The model is build up based on the LCEA methodology and model itself can simulate the aging and breakage of pipes through the target life cycle. In addition the hydraulic analysis program EPANET2.0 is linked to developed model to analyze hydraulic factors. Developed model is applied to two WDSs which are A WDS and B WDS. Model runs for 1yr to maximum 100yr target life cycle for both WDSs to check the energy tendency as well as to determine optimal life cycle. Results show that 40yr and 54yr as optimal life cycle for each WDS, and tendency shows the effective energy is keep changing according to the target life cycle. Introduced methodology is expected to use as an alternative option for determining life cycle of WDS.

• 환경생물
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• 제38권1호
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• pp.179-188
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• 2020

The influx of marine exotic and alien species is disrupting marine ecosystems and aquaculture. Herdmania momus, reported as an invasive species, is distributed all along the coast of Jeju Island and has been confirmed to be distributed and spread to Busan. The potential habitats and distribution of H. momus were estimated using the maximum entropy (MaxEnt) model, quantum geographic information system (QGIS), and Bio-ocean rasters for analysis of climate and environment(Bio-ORACLE), which can predict the distribution and spread based only on species occurrence data using species distribution model (SDM). Temperature and salinity were selected as environmental variables based on previous literature. Additionally, two different representative concentration pathway (RCP) scenarios (RCP 4.5 and RCP 8.5) were set up to estimate future and potential habitats owing to climate change. The prediction of potential habitats and distribution for H. momus using MaxEnt confirmed maximum temperature as the highest contributor(77.1%), and mean salinity, the lowest (0%). And the potential habitats and distribution of H. momus were the highest on Jeju Island, and no potential habitat or distribution was seen in the Yellow Sea. Different RCP scenarios showed that at RCP 4.5, H. momus would be distributed along the coast of Jeju Island in the year 2050 and that the distribution would expand to parts of the Korea Strait by the year 2100. RCP 8.5, the distribution in 2050 is predicted to be similar to that at RCP 4.5; however, by 2100, the distribution is predicted to expand to parts of the Korea Strait and the East Sea. This study can be utilized as basic data to effectively control the ecological injuries by H. momus by predicting its spread and distribution both at present and in the future.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 A
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• pp.61-63
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• 2000

As increasing the failure of distribution transformers, we need to manage them efficiently. This paper proposes the method for distribution transformer's management using loss-of-life calculation. The Data Acquisition System(DAS) was developed to manage transformers and the HDLC protocol applied to the system. It will be feasible application to diagnose distribution transformers by checking load conditions such as top oil temperature, ambient temperature, load current, etc. and using loss-of-life calculation.

• 동력기계공학회지
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• 제20권3호
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• pp.29-35
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• 2016

Because of the severe service environment of the large marine vessel, the fatigue strength and its evaluation play an important role in design and maintenance of marine crankshaft. The aim of this work is to investigate the probability distribution of fatigue lives in crank throw forged steel and to develop the methodology for estimation of the probabilistic design fatigue strength. Detailed studies were performed on the constant amplitude axial loading fatigue test. The experiments were controlled by stress ratio of -1 and 15Hz frequency for each stress level. The considerable variability of fatigue life was observed in each stress level under rigidly controlled constant fatigue testing conditions. The fatigue life of crank throw forged steel was well followed the log-normal and Weibull distribution. In addition, it can be used for the estimation of probabilistic design fatigue strength by using the proposed methodology.

• 한국생산제조학회지
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• 제18권4호
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• pp.395-400
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• 2009

As the variables affecting the fatigue behavior have uncertainty, the fatigue crack propagation is stochastic in nature. Therefore, the fatigue life prediction is critical for the design and the maintenance of many structural components. In this study, fatigue experiments are conducted on the specimens of magnesium alloy under the different thicknesses of specimen. The effects of specimen thickness on the probability distribution of the fatigue crack propagation life and the crack size are estimated experimentally. The probability distribution of the crack size and the fatigue life for different specimen thicknesses are investigated by Anderson-Darling test and the best fit for those probability distributions are also presented.

• 한국정밀공학회지
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• 제15권6호
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• pp.90-96
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• 1998

Helical gear system is widely used to transmit heavy duty power with harmonies and silences between parallel shafts. This paper predicts a life with Weibull distribution and estimates a reliability based on recycle principle of helical gear systems. 2-parameter Weibull distribution is generally adopted to estimate the mechanical life and the reliability of most gear systems, because this Weibull distribution is proper to explain a characteristics or a life of parts of gear systems with linearity of probability density data on weibull data sheet. For a high reliability, this paper estimates a number of overhaul times and a number of needed substitutes (exchange attachment,1 or parts) with following renewal theory, One is make an exchange of whole module include failure attachments/parts and second estimating method is only exchange of a failure attachments / parts.

• 대한기계학회논문집A
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• 제27권12호
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• pp.2004-2010
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• 2003

Fracture life and crack retardation behavior were examined experimentally using CT specimens of aluminum alloy 5083. Crack retardation life and fracture life were a wide difference. between 0.8 and 0.6 in proportion to ratio of load reduction. The wheeler model retardation parameter was used successfully to predict crack growth behavior. By using a crack propagation rule, prediction of fracture life can be evaluated quantitatively. A statistical approach based on Weibull distribution was applied to the test data to evaluate the dispersion in the retardation life and fracture life by the change of load reduction.

• Communications for Statistical Applications and Methods
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• 제23권4호
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• pp.269-285
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• 2016

In this paper, a simple step-stress accelerated life test (ALT) under progressive type-II censoring is considered. Progressive type-II censoring and accelerated life testing are provided to decrease the lifetime of testing and lower test expenses. The cumulative exposure model is assumed when the lifetime of test units follows an extension of the exponential distribution. Maximum likelihood estimates (MLEs) and Bayes estimates (BEs) of the model parameters are also obtained. In addition, a real dataset is analyzed to illustrate the proposed procedures. Approximate, bootstrap and credible confidence intervals (CIs) of the estimators are then derived. Finally, the accuracy of the MLEs and BEs for the model parameters is investigated through simulation studies.

• 한국신뢰성학회지:신뢰성응용연구
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• 제16권4호
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• pp.280-286
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• 2016

Purpose: Recently, Jiang defines the tradeoff B life to minimize a sum of life lost by preventive maintenance (PM) and corrective maintenance (CM) contribution parts and sets up an optimal replacement age of age replacement policy as this tradeoff life. In this paper, Jiang's model only considering the known lifetime distribution is extended by assigning different weights to two parts of PM and CM in order to reflect the practical maintenance situations in application. Methods: The new age replacement model is formulated and the meaning of a weight factor is expressed with the implied cost of failure under asymptotic expected cost model and also discussed with one-cycle expected cost criterion. Results: The proposed model is applied to Weibull and lognormal lifetime distributions and optimum PM replacement ages are derived with corresponding implied cost of failure. Conclusion: The new age replacement policy to escape the estimation of cost of failure in classical asymptotic expected cost criterion based on the renewal process is provided.

• 대한기계학회논문집A
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• 제32권12호
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• pp.1055-1062
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• 2008

Engineering materials have been studied and developed remarkably for a long time. But, few reports about marine propeller materials are presented. Recently, some researchers have studied the material strength of marine propellers. However, studies on parametric sensitivity and probabilistic distribution of fatigue life of propeller materials have not been made yet. In this study, a method to predict the probabilistic distributions of fatigue life of propeller materials is presented, and the influence of several parameters on the life distribution is discussed.